On 13/04/2018 5:25 PM, Volker Simonis wrote:
On Thu, Apr 12, 2018 at 11:30 PM, David Holmes <david.hol...@oracle.com> wrote:
On 12/04/2018 11:33 PM, Magnus Ihse Bursie wrote:
On 2018-04-12 14:15, David Holmes wrote:
Hi Magnus,
On 12/04/2018 9:39 PM, Magnus Ihse Bursie wrote:
It is currently easy to add new JVM features to the JVM build, but it is
not possible to remove features.
With this change, features can be both added or removed from the default
set. They are added using --with-jvm-features=f1,f2 and removed using
--with-jvm-features=-f1,-f2. The syntax can be combined, so
--with-jvm-features=dtrace,-nmt will enable dtrace but disable native memory
tracking.
I need to point out that we have never tested disabling individual VM
features likes this. They are either all on, or all off for the minimal VM!
There may be implicit dependencies between features.
Well, I have. :-) However, I don't do that regularly, and changes might
very well have crept in. As always, if you build something non-standard that
is not regularly tested, you're on your own.
Feels to me like you've taken away the safety-fence and are encouraging
people to attempt these unsupported configurations. Whether that was your
intent or not.
I think that would be great. If people would try out different
configurations AND fix them that would be a great code clean-up for
HotSpot. I've recently tried various "unsupported" configurations
(i.e. minimal plus some selected features) and found that the
resulting build failures are mostly artificial because the
corresponding features aren't correctly ifdefed.
These features were never expected to be individually selectable. The
minimal VM was a special case. There is likely more work needed than
just build time ifdefs to allow this to actually work.
For fun try building on 64-bit and ask for no compiler2 to see what
happens. It makes no sense. But there are no constraints implemented so
you can ask for nonsensical things. That's not a good thing in my book.
David
-----
In any case, the purpose of this is not so much to disable existing JVM
features (after all, no one has really been missing this functionality), as
to pave the way for the upcoming patch for including/excluding individual
GCs.
Surely a GC selection flag would have sufficed.
David
/Magnus
David
I also included some additional code cleanup and fixes, such as printing
the JVM feature set at the summary.
Bug: https://bugs.openjdk.java.net/browse/JDK-8201483
WebRev:
http://cr.openjdk.java.net/~ihse/JDK-8201483-disable-JVM-features/webrev.01
